Trihexyphenidyl – Patient Information for Australia
Basic Product Information
| International Non-Proprietary Name (INN) | Trihexyphenidyl |
|---|---|
| Australia Brand Names | Artane®, Apo-Trihexyphenidyl |
| ATC Code | N04AA01 |
| Available Forms & Strengths | Tablets: 2 mg, 5 mg; Oral solution: 2 mg/5 mL |
| Manufacturers | Pfizer Australia, Apotex, Sigma Pharmaceuticals, various generics |
| Prescription Status | Prescription only medicine (Schedule 4, S4) – Not available as a Pharmacy Medicine (S2/S3) or over-the-counter in Australia |
Mechanism of Action
In simple terms: Trihexyphenidyl works by blocking certain natural chemicals in the brain called acetylcholine, helping to restore a healthy balance with another brain chemical called dopamine. This assists with reducing symptoms such as muscle stiffness, tremor, and spasms, particularly in conditions like Parkinson’s disease.
For healthcare professionals: Trihexyphenidyl is a centrally acting antimuscarinic (anticholinergic) agent. It selectively blocks muscarinic receptors in the central nervous system, decreasing cholinergic activity that becomes relatively excessive when dopaminergic activity is diminished (as in Parkinson’s disease). This, in turn, rebalances neurotransmitter activity within the nigrostriatal pathway.
Pharmacokinetics
- Absorption: Rapid, with oral bioavailability up to 90%.
- Peak plasma concentration: Usually within 1–2 hours after dosing.
- Metabolism: Hepatic (through the liver), with substantial first-pass effect.
- Elimination: Mainly excreted via the kidneys as metabolites.
- Duration of Action: Typically 6–12 hours; some effects may last up to 24 hours.
Use in Everyday Life and Best Practices
Trihexyphenidyl is commonly prescribed in Australia for managing Parkinson’s disease symptoms (especially tremor and rigidity), and to control involuntary movements (extrapyramidal symptoms) caused by certain medications. Always take this medication as prescribed by your doctor. Tablets can be taken with water. Oral solutions should be measured using a medicine spoon or syringe for accuracy.
- Usual adult dose: 1 mg to 2 mg once or twice daily, gradually increased as needed (up to a maximum of 12–15 mg daily, in divided doses).
- A typical maintenance dose is 5–10 mg daily in 3 or 4 divided doses.
- If you miss a dose, take it as soon as you remember, unless it is almost time for your next dose.
- Do not stop suddenly unless advised by your doctor, as symptoms may worsen.
Dosing: Morning vs Evening
- Trihexyphenidyl may be taken in the morning or evening, but dividing the dose can help reduce side effects.
- Morning dosing: Can help control daytime symptoms like tremor. May cause less sleep disturbance.
- Evening dosing: May be considered if symptoms are worse at night, but may lead to dry mouth, difficulty sleeping, or confusion (especially in older adults).
- Tip: Try to take your doses at the same time(s) every day for best effect.
Taking with Food, or on an Empty Stomach
- Trihexyphenidyl can be taken with or without food.
- With food: Taking with meals may reduce the risk of stomach upset, a common side effect.
- Empty stomach: May result in faster onset of action but can increase risk of nausea.
- Australian dietary advice: No special dietary restrictions. Eating regular, balanced meals and staying hydrated is important, especially in hot climates, given the medicine's potential to reduce sweating and increase risk of heat stress.
Interaction Warnings
| Interaction | Advice |
|---|---|
| Food | No major interactions; take with food to reduce stomach upset if needed. |
| Alcohol | Avoid or limit alcohol; may increase sedation and confusion. |
| Other anticholinergic drugs (e.g. antihistamines, antidepressants, antipsychotics) | May increase the risk of side effects such as dry mouth, dizziness, constipation, confusion. |
| Levodopa | May be used together under supervision for Parkinson’s disease; dose adjustment may be required. |
| Other CNS depressants | Increased risk of drowsiness, confusion, falls (particularly in the elderly). |
Indications
| Indication | Status | Notes |
|---|---|---|
| Parkinson’s disease (idiopathic and post-encephalitic) | Approved | Used as adjunct to other therapies or on its own for tremor and rigidity |
| Drug-induced extrapyramidal symptoms (excluding tardive dyskinesia) | Approved | Particularly with antipsychotic medications |
| Dystonia, other movement disorders | Off-label | May be used under specialist guidance |
Dosing According to Clinical Indications
| Indication | Adults | Children | Elderly |
|---|---|---|---|
| Parkinson’s disease | Start at 1 mg once daily; increase by 2 mg every 3–5 days, up to 6–10 mg/day in divided doses (max 15 mg/day) | Rarely used; specialist advice essential. Typical: 0.1–0.2 mg/kg in divided doses | Start low, go slow. Increased risk of confusion, delirium; monitor carefully |
| Drug-induced extrapyramidal symptoms | 1–2 mg 2–3 times daily; adjust as needed | Specialist advice | Half adult dose may be appropriate |
Safety Profile and Possible Side Effects
| Frequency | Side Effects | Advice |
|---|---|---|
| Common | Dry mouth, blurred vision, constipation, drowsiness, dizziness, nausea, urinary retention | Usually mild; report if severe or persistent |
| Less common | Confusion, hallucinations, impaired memory, agitation, difficulty urinating (especially in older people), tachycardia | More likely at higher doses or in elderly |
| Rare but serious | Heat stroke (due to decreased sweating), glaucoma, paradoxical bradycardia, allergic reaction | Seek immediate medical attention if these occur |
Guidelines for Proper Use – Australian Context
- Always take exactly as prescribed, and never share your medication with others.
- Monitor for side effects; talk to your doctor or pharmacist if you develop confusion, vision changes, or difficult urination.
- Be careful driving or operating machinery until you know how the medication affects you.
- Drink adequate water and avoid overheating, especially outdoors in Australian summer, as the medication can reduce your ability to sweat.
- Keep up with regular reviews; do not alter or stop the dose abruptly except on medical advice.
- Store out of reach of children, at room temperature (below 25°C), away from moisture and direct sunlight.
Alternative Treatment Options (PBS-Listed Comparisons)
- Levodopa/carbidopa (PBS listed): Considered the gold standard for Parkinson’s disease. More effective for rigidity and bradykinesia than for tremor. May cause motor fluctuations over time.
- Benztropine: Another anticholinergic for similar indications; comparable risk of cognitive effects, especially in the elderly.
- Amantadine: Antiviral with mild antiparkinsonian effects; can cause ankle swelling, livedo reticularis (skin discolouration), insomnia.
- Dopamine agonists (e.g. pramipexole, PBS listed): Useful adjuncts or alternatives. Risk of impulse-control disorders, sleep attacks, hallucinations in older adults.
- Deep brain stimulation: Surgical option for patients not responding to medications. Used under specialist care.
- Non-pharmaceutical therapies: Exercise (physiotherapy), speech therapy, occupational therapy.
Trihexyphenidyl is rarely used as first-line treatment in Australia due to side effects, especially in those over 60 years. Its use is mainly for younger patients with predominant tremor, or for managing drug-induced movement problems.
Legal, Registration & Reimbursement Status in Australia
- Registered with: Therapeutic Goods Administration (TGA; ARTG entry available)
- Prescription requirements: S4 (Prescription Only) – can only be dispensed by a pharmacist on a valid prescription
- Reimbursement: Not currently listed on the PBS for idiopathic Parkinson’s disease as monotherapy, though benztropine is. For drug-induced movement disorders, discuss with your healthcare provider about cost and eligibility for subsidised schemes
- Import and supply: Subject to TGA and state/territory regulations on controlled substances
Latest Research and Clinical Guidance (2022–2025)
- Guidelines (Movement Disorder Society, Australian Therapeutic Guidelines): Trihexyphenidyl remains a useful option for tremor-dominant Parkinson’s when other medications are not tolerated or effective, but should be avoided in people over 60 due to cognitive risks (Therapeutic Guidelines: Neurology, 2024 update).
- Cognitive Effects: 2023 European/Australian studies emphasise heightened vigilance for delirium and memory problems, especially in older adults or those with existing cognitive impairment.
- Pediatric Dystonia: Limited use in Australian paediatric services for dystonic conditions, under neurologist supervision (Rineer et al., 2023; MDS practice guidelines, 2024).
- Drug Interactions: Australian Prescriber (2023) highlights risks when used with other anticholinergic medications or cholinesterase inhibitors.
- Summary: Use has declined in recent Australian practice in favour of agents with a more favourable safety profile in elderly patients.
Availability and Delivery in Australia
| Pack Size | Typical Price (AUD)* | Expected Pharmacy Delivery Times |
|---|---|---|
| 100 tablets (2 mg or 5 mg) | $25–40 |
|
| Oral solution: 100 mL | $30–40 | Similar to tablets |
*Prices are indicative and can vary between pharmacies. Medication supply may be subject to export restrictions or supply chain issues in some regions.
Frequently Asked Questions (FAQ)
- Can I drive while taking Trihexyphenidyl?
Answer: Trihexyphenidyl can cause drowsiness, blurred vision, and confusion in some people. Until you know how you react, avoid driving or operating heavy machinery. - What should I do if I miss a dose?
Answer: Take it as soon as you remember unless it's almost time for your next dose. Do not take two doses together to make up for a missed dose. - Is Trihexyphenidyl safe in pregnancy or breastfeeding?
Answer: Safety in pregnancy and breastfeeding is not well established. Use only if prescribed by your doctor, who will weigh the risks and benefits. - Can I take Trihexyphenidyl with my regular medications?
Answer: Inform your doctor and pharmacist about all other medications you are taking (including over-the-counter, herbal, and supplements) to avoid interactions, especially with other drugs affecting the central nervous system. - What are the most important side effects to watch for?
Answer: Seek medical attention if you notice confusion, severe constipation, difficulty urinating, sudden vision changes, or signs of heat stress (such as overheating, sweating less than usual, or weakness in hot weather).
Always seek advice from your doctor or pharmacy team if you have any concerns or experience unusual symptoms.
